1. Field of the Invention
This invention relates to a process in which uranium extracted to an organic solvent is stripped and recovered from an organic phase to an aqueous phase.
2. Description of the Prior Arts
Conventionally Amex process using alkyl amine and Purex process using neutral phosphoric acid ester are well known as a process for separation and purification of uranium existing in an aqueous solution. In the former, uranium in an aqueous solution is extracted into an organic phase as uranyl sulphate by using an organic solvent containing alkyl amine and after conversion of the extracted uranyl sulphate to uranyl chloride with contact of hydrochloric acid, the resultant uranyl chloride is stripped to the aqueous phase with contact of water. While, the latter is a typical process used for retreatment process of nuclear fuel. In this process uranyl nitrate and uranous nitrate are extracted and plutonium is separated after conversion of its valency. The extracted uranyl nitrate is separated and purified from the other ions by stripping from the organic phase to the aqueous phase with contact of water.
These processes, however, have the following disadvantage. The aqueous strip solution containing uranium value is neutralized with NH.sub.3 or uranium is precipitated and filtered as UF.sub.4 by addition of HF after reduction process and consequently the filtrate after recovery of uranium value as a solid must be discharged out from the system.
In production of phosphoric acid by wet process, an aqueous solution (crude phosphoric acid) obtained by dissolution of phosphorus ore with H.sub.2 SO.sub.4 generally contains about 0.1 g/l of uranium. U.S. Pat. Nos. 3,711,591 and 3,835,214 disclose well known processes for recovery of uranium from the crude phosphoric acid. In the former uranium in the phosphoric acid solution is oxidised to U.sup.6+ ion, while in the latter uranium is reduced to U.sup.4+ ion. Uranium in both processes is extracted by organic solvent and stripped to the aqueous phase after conversion of valency of uranium extracted in the organic phase by either reduction or oxidation.
These processes have the following disadvantages:
(1) Operation is complicate.
(2) Phosphoric acid solution after extraction of uranium is contaminated by iron and NaClO.sub.3 using for conversion of uranium ion valency.
(3) One additive process is needed to treat the aqueous solution containing uranium after stripping stage.
Japanese Laid-Open Patent Application Sho 53-128596 discloses a process proposed to overcome the disadvantages of U.S. patents described above. In this patent application U.sup.6+ and U.sup.4+ ions in the aqueous solution (crude phosphoric acid) can be extracted using mixture of extractants used in the above U.S. patents and this process is different from U.S. patents processes in that it uses H.sub.2 SO.sub.4 +HF mixture in order to strip uranium in the organic phase to the aqueous phase. In this process the stripped uranium value can be filtered and recovered as a precipitate of uranium fluoride and consequently the total process is shortened. However, in the stripping stage HF in the strip solution (HF+H.sub.2 SO.sub.4) is extracted to the organic phase by 0.02-0.04M tri-octyl phosphine oxide (TOPO) using as an extractant and this HF in the organic phase contaminates phosphoric acid solution with contact of crude phosphoric acid and the organic solvent. The contamination of phosphoric acid by HF and large loss of HF reduce an economical value of this process.